This is the third achievement you'll unlock. There is no way you can miss this.
After you break out of Abstergo and get the achievement for it, you will be in a brand new place. It's pretty straight-forward what you have to do here, just follow Lucy up the metal slopes to the right. At the top, you and Lucy will go down a hallway and take the next right. You both will enter a room that has two new people, Sean and Rebecca.
Watch the cutscene that plays, and then you will see a red chair--the "upgraded" version of the Animus. You can hop right onto the Animus 2.0, or you can talk to Lucy two times, Sean once, and Rebecca once. (It appears as though there is no achievement like the first game's "Conversationalist," but if you want more information about the story, feel free to speak to them). Whatever you did, you will unlock this achievement as soon as you get on the Animus 2.0.